Question

When a charged particle moves perpendicular to a magnetic field, then

• A. Speed of the particle is changed.
• B. Speed of the particle remains unchanged.
• C. Direction of the particle remains unchanged.
• D. Acceleration of the particle remains unchanged.

Answer 1

Answer: (B)

Speed of the particle remains unchanged.

The force on a charged particle moving in magnetic field is given by

$\overrightarrow{F}=q\overrightarrow{v}\times \overrightarrow{B}$

When the velocity is perpendicular to the magnetic field, the magnetic force is perpendicular to both of them, and particle moves in circle with constant speed $v$.